Dithiobis



United States Patent C) 3,297,713 DIII-HOBISM-PHENYLMALEIMIDES) Elbert C. Ladd, Passaic, N.J., assignor to United States Rubber Company, New York, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 30, 1962, Ser. No. 183,754

3 Claims. (Cl. 26tl326.3)

This invention relates to a new class of chemicals, denoted as symmetrical dithiobis(N-phenylmaleimides) and to the method of preparing same. In addition, the invention relates to the use of these novel compounds as vulcanizing agents for rubber.

The subject compounds may be represented by the following formula:

The compounds of this invention may be used as vulcanizing agents for natural and synthetic rubbers having high olefinic unsaturation. Furthermore, rubber stocks cured by the subject compounds exhibit improved resistance to wear and cut-growth when compared with similar Patented Jan. 10, 1967 stocks cured by known bismaleimide-type compounds. The rubber is compounded in the conventional way with from 0.25 to 6.0 parts by weight, and preferably from 1.5 to 2.5 parts by weight, of the subject compounds per parts of rubber, together with other conventional compounding agents, typically carbon black and an oily plasticizer, after which the stock is shaped and vulcanized in the manner well-known for the vulcanization of rubber. The subject compounds may be used as the sole vulcanizing agent or cojointly with other vulcanizing agents or accelerating agents.

The rubbers which are operable in this invention are the natural and the synthetic rubbers which have high olefinic unsaturation and which are conventionally vulcanized with sulfur. Such synthetic rubbers are the homopolymers of aliphatic conjugated diolefin hydrocarbons and copolymers of such diolefins with monoolefins compounds copolymerizable therewith. Such monoolefins include styrene; alpha-methylstyrene; p-methylstyrene; alpha, p-dimethylstyrene; acrylic and methacrylic nitriles, amides, acids and esters; vinyl pyridines; fumaric esters; methylenemalonic esters; vinylidene chloride; methyl vinyl ketoneyand methyl isopropenyl ketone. Mixtures of such monoolefinic compounds can also be copolymerized with the diolefin. The term high olefinic unsaturation here connotes an amount of unsaturation on the order of that occurring in Hevea rubber. The copolymers must contain copolymerized therein at least about 35% of the diolefin hydrocarbon. The butyl rubbers, which are elastome-rs made by an ionic polymerization process, from a major amount of an isoolefin and a minor amount of a conjugated diolefin hydrocarbon in an organic solvent, are not curable with maleimides, and are excluded from the scope of the invention.

The synthetic rubbers referred to may be either emulsion polymers or stereospecific (or stereoregular) homopolymers and copolymers of aliphatic conjugated diolefin hydrocarbons, of which the polymers of greatest commercial interest now are cis-l,4-polyisoprene (often called synthetic natural rubber) and cis-l,4-polybutadiene.

The following examples illustrate the invention:

EXAMPLE I Step 1.Preparati0n 0 a bismaleamic acid Calculated, 6.3% Found, 6.27% N.

Step 2.-C0nversi0n of the bismaleamz'c acid to a bismaleimide In a 500 ml. flask, a mixture of 88 grams of the above bismaleamic acid, 200 grams of acetic anhydrde and 4 grams of sodium acetate was heated to 9095 C. for 20 minutes. The reaction mixture was poured into water resulting in a green colored product which had a melting range of l52 C. After several recrystallizations from benzene, a nearly white product was obtained which 3 had a melting point of 171-173 C. and was identified as 2,2-dithiobis (N-phenylmaleimide) Analysis for C20H12N2S204:

Calculated Found Percent N 6.86 6.82 Percent S 15. 68 15.10

EXAMPLE II This example demonstrates the use of 2,2'-dithiobis- (N-phenylmaleimide) as a vulcanizing agent. A commercial styrene-butadiene copolymer rubber (SBR) with a styrene content of about 20 percent (SBR-1500) was compounded with 50 parts, per hundred of rubber, of a high abrasion furnace black (marketed under the registered trademark, Philblack O, by the Phillips Chemical Co.), 7.5 parts of a naphthenic type oil, and 1.9 parts of 2,2-dithiobis(N-phenylmaleimide). By way of comparison, a similar sample was prepared by replacing the 2,2'-dithiobis(N phenylmaleimide) with N,N'-m-phenylenebismaleimide, a known vulcanizing agent. Compounding was done in the conventional manner. The rubber, black and oil were assembled and mixed in a Banbury mixer for minutes. Discharge temperatures was 275 300 F. The vulcanizing agent was added on a cool tworoll mill. Samples were cured in a press at several temperatures and times as indicated below, and tested by the conventional testing methods used for rubber.

1 Circosol 2xHa mixture of comparatively high molecular weight hydrocarbons, sp. gr., 0.9465' aniline polnt, 175 F. (Sun Oil Co.

1 Added to the mix in the form of a paste [equal weights of 2,2-dithiob1s- (N-pheny lmaleimide) and 160-180 oil].

The following table shows the results of tests on the cured samples.

Time of Temp. of Physical Properties Cure Cure F.) 1 2 (minutes) Tensile Strength (p.s.i.) 120 300 1, 200 675 30 350 1, 800 975 10 400 1, 800 1, 585 5 450 1, 750 2, 000 Elongation at Break (per- 120 300 430 510 cent 30 350 315 460 10 400 220 450 5 450 175 430 Modulus 2133007 (p.s.i.) 120 300 675 400 30 350 1, 675 575 10 400 1 2,900 875 5 450 l 3, 525 1, 200

1 Extrapolated value.

EXAMPLE III Stock 3 4 5 6 SB R-1500 100 100 100 100 HAF carbon black 50 50 50 Naphthenic type oil 7. 5 7. 5 7. 5 7. 5 2,2-dithiobis(Nphenylmaleimr e 1. 8 1. 8 N,N-m-phenylene bismaleimjde 1. 8 1.8 2,2-dibenz0thiazyl disulfide 1. 0 1. O

Dicumyl peroxide 0. 7 0.7

1 Added to the mix in the form of a paste pts. 01 N,N-m-phenylene bismaleimide and 45 pts. of 160-180 oil).

The following table shows the results of tests on the cured samples. The cut-growth is measured essentially as described by E. E. Auer et al., Rubber Chem. & Tech. 31, 185 (1958), Factors Affecting Laboratory Cut- Growth Resistance of Cold SBR Tread Stocks. The units are kilocycles per inch growth.

Time of Temp. 01 Physical Properties Cure Cure 3 4 5 6 (minutes) F.)

Unaged:

Tensile Strength (p.s.i.) 300 2, 305 2, 365 2, 555 2, 455 15 350 2, 340 2, 285 2, 485 2, 585 3 400 2, 005 2, 095 2, 425 2, 090 Elongation at Break (percent) 90 300 480 400 500 480 15 350 460 410 490 470 3 400 370 400 480 460 Modulus at 200% (p.s.i.) 90 300 500 625 535 640 15 350 480 550 545 615 3 400 455 490 560 575 Modulus at 300% (p.s.i.) 90 300 1,050 1,300 1,100 1, 250 15 350 1, 025 1, 240 1,130 1, 240 3 400 985 1, 050 1, 175 1, 200 Cut-growth at 150 F. (ke./ineh 90 300 46. 5 25.8 17. 1 8. 7 growth). 15 350 50. 6 37. 8 17. 0 6. 1 3 400 40. 5 28. 3 15. 4 9. 4 Aged-2 days in air at 212 F.:

Tensile Strength (p.s.i.) 90 300 2, 380 2, 400 2, 720 2, 640 15 350 2, 210 2, 400 2, 610 2, 430 3 400 2, 060 2, 2, 500 2, 190 Elongation at Break (percent) 90 300 420 360 450 430 15 350 390 370 410 410 3 400 370 350 410 390 Modulus at 200% (p.s.i.) 90 300 660 800 725 775 15 350 725 790 735 800 3 400 750 775 785 780 Modulus at 300% (p.s.i.) 90 300 1, 375 1, 750 1, 400 1, 475 15 350 1, 475 1, 640 1, 450 1, 525 3 400 1, 500 l, 610 1, 550 1, 500 Cut-growth at F. (km/inch 90 300 25. 1 16. 4 7. 8 5. 5 growth). 15 350 25. 0 22. 2 8. 9 5. 2 3 400 16. 0 14. 2 5. 4 6. 5

, Time 01 Temp. 01 p Physical Pro erties Cure Cure 3 '4 5 6 (minutes) F.) l

. 1 Aged-6 days in air at 212 F.:

Tensile strength (p.s.i.) 90 300 2, 220 2, 190 2, 320 2, 630 350 2, 290 2, 090 2, 660 2, 520 3 400 1, 950 1, 930 2, 490 2, 460 Elongation at Break (percent 90 300 330 310 350 420 15 350 340 220 360 390 3 400 300 300 350 370 Modulus at 200% (p.s.i 90 300 925 1, 000 890 s75 15 350 960 975 925 885 3 4.0.1 975 950 950 900 Modulus at 300% (p.s.1 90 300 1, 8 1 1, 975 1, 700 1, G25 15 350 1,890 1 1, 900 1,775 1, 650 3 400 1, 950 1 1, 875 1,825 1,775 Cut-growth at 150 F. (kc/inch 90 300 16.6 0.3 6.1 8.9 growth). 15 350 18. 1 l1. 5 6. 2 8. 6 3 400 21.8 8.8 3.8 5.5

1 Extrapolated value.

The above examples, by comparison with Example II, shOW the spectacular acceleration of the dithio-imide cure Time (mills) by means of an accelerator such as 2,2-di benzothiazyl Physlcallmpertles 3 5? 5 6 7 8 disulfide or dicumy-l peroxide. Data also show that rubber stocks mired wlth the Chemlcal ur.m.vent10n not only Tensile Strength (p.s.i.) 22 2.115 2,055 2, 405 2,055 age 1n air equally as well as b1SlII1al6l1'I11d cured rubber 45 1, 990 2,165 2. 505 2,265 90 1,670 2,310 2, 550 2, 390 stocks, but the cured stocks have vastly improved cut 25 Elongation atBreak (Pen 22 460 440 460 500 growth properties. cent). 45 370 410 450 480 M d 1 t 7 90 350 410 450 47g 0 uusa 200 13.5.1. 22 525 525 550 51 EXAMPLE IV a 45 075 610 620 530 90 775 750 665 590 This example 1s similar to Example III and demon- Reiame Abrasion 22 7 ,4 70, 68.7 59.8 strates that rubber stocks cured with the chemicals of Reslstance- 7956 820 59.0 84.2 74.7 66.4 thls lnvention, in presence of either a peroxide or a thiazoletype accelerator, are better with respect to abrasion resistance than corresponding stocks which are accelerated EXAMPLE V 1 t and gl w :23: 5: gs g sg i g z g i 23 35 This example demonstrates that 4,4'-d1th1obis(N-phenpoun mg i 6 ylmaleimide) is equally as efiective as 2,2-ditl1iobis(N- manner asm Xamp 6 phenylmaleimide) as a vulcanizing agent for rubber. Further, the example shows that it is possible to accelerate the 4,4-dithiobis(N-phenylrnaleimide) cure of SBR by Partsbyvveight 4,0 the use of either 2,2-dibenzothiazyl disulfide or dicumyl peroxide as the accelerating agent. Compounding and Stock 5 l 6 I 7 l 8 processing were carried out in the same manner as in Example II.

IBROO. B1 IE .c

AF arbou ac Naphthenic type 011 Parts by Wmght 2,2-dithiobis(li-phelylmaleimzldez N,N-m-pheny ene isma eimi e 2,2-dibenz0thiazyl disulfidevn Stock 9 10 11 12 13 Dicumyl peroxide.

SBR -1500 100 100 100 100 Added to the mix in the form of apastc (50 parts ofN,N-m-pheny1en 50 g i fggg gg gg 5 g 5 .9 5 g 5 5 bismaleimide and 50 parts of 160-180 011). 4,4l dithi bi (N phenylmaleirnide. 2. 0 2.0 2. 0 N,N1-m-pleuylene bis- 1 0 The following table shows the results of tests on the g ggfifi ifl fifif fifij 2 cured samples. The Relative Abrasion Resistance value 55 Dicumyl peroxide is a relative rating obtained by comparing the weight loss of a standard compound (rated 100) with the weight loss of the test compound.

The following table shows the results of tests on the cured samples.

Time (mins.) Physical Properties of Cure at 9 10 11 12 13 Tensile Strength (p.s.i.) 22 675 1, 275 1, 785 1,925 1, $35 45 1, 350 1, 275 2,010 2, 050 1, 950 Elongation at Break (percent) 22 645 235 410 340 330 45 945 220 390 335 'c 15 Modulus at 300% (psi 22 300 1 1,825 1, 1,625 1, $35 45 575 1 2, 050 1, 375 1, 725 1, 775

1 Extrapolated value.

2'-dithi0bis (N-phenylmaleimide) 4-dithi0bis (N-phenylmaleimide) i l-CH E-lH References Cited by the Examiner UNITED STATES PATENTS Funz 260-79.5 Himel et a1. 26079.5 Sauers et al. 260-3263 Ladd 260326.3

ALEX MAZEL, Primary Examiner.

10 WILLIAM H. SHORT, Examiner.

M. P. HENDRICKSON, I. TOVAR, Assistant Examiners. 

1. SYMMETRICAL DITHIOBIS(N-PHENYLMALEIMIDE) HAVING THE FORMULA: 